Monorail systems provide the most economy when loading and discharge points are constantly changing and where distances exceed several hundred feet. Monorail support sections can be set on almost any type of terrain-over mud, water and superstructures or through trenches and tunnels. Over the monorails self-propelled hopper cars travel unattended from loading points to points of discharge where they automatically stop. An innovation introduced during the mid- 1960's uses a truck or trailer-mounted unit, similar to the one shown, which is a combination concrete materials transporter and proportioning-mixing plant. Separate ingredients- cement, sand, stone or gravel, and water- are transported in compartmented bins and tanks in bulk form. The ingredients are not proportioned and mixed until the unit arrives at the delivery point. Upon arrival the operator, using a predetermined mix settings chart, sets dials for the required concrete mix design proportions. Production and discharge of concrete starts at once. Cement is introduced into the mix at a constant rate by means of a rotary meter-feeder. Sand and stone or gravel are ribbon-fed separately into the mix at a rate that may be varied by adjusting fine and coarse aggregate proportioning dials. Water is metered by a hand controlled valve. Thus, with a single constant (cement) and three variables- fine aggregate, coarse aggregate, and water- any desired combination of ingredients may be obtained. Also, the operator may, immediately upon advice of a revised specification, change the amount of water going into the mix, thus changing the slump of the concrete being produced. Mixing occurs continuously only as delivery is being made. The ingredients flow in the selected proportions into a mix conveyor mechanism which consists of a rapidly revolving, hydraulically driven mixing helicoid conveyor mounted in a flexible D-shaped trough. Mixing action may be continuous or intermittent until the supply of materials on board is depleted. In continuous production, concrete is proportioned and mixed at the delivery rate of a cubic yard every one to four minutes depending on the cement content of the concrete mix design and the model of the unit. The mixed concrete is conveyed into a conventional delivery chute for discharge. Units are available with` capacities to transport sufficient unmixed material to produce four, six, eight or ten cubic yards of concrete.